The invention relates to adjusting apparatus in general, and more particularly to improvements in apparatus which can be used with advantage for forward and rearward adjustment of seats in vehicles, for example, of the driver's seat or of the seat next to the driver's seat in a motor vehicle.
It is known to install a seat in a motor vehicle in such a way that the entire seat can be shifted forwardly or backwards for convenience of a short- or long-legged driver or passenger and/or to provide more room for the legs of the occupant or occupants of a rear seat. As a rule, the floor of the passenger compartment is provided with a pair of spaced-apart guide rails which extend in the longitudinal direction of the vehicle and serve to support and guide second rails which are provided at the underside of the body-supporting portion of the seat. One set of rails is provided with toothed racks and the other set of rails supports pinions which mate with the adjacent racks and are connected to each other by a transversely extending torque-transmitting shaft. The shaft can be rotated by the output element of a motor-driven transmission. The motor and transmission are connected with those rails which carry the pinions and their shaft.
An adjusting apparatus of the above outlined character is disclosed, for example, in German Offenlegungsschrift No. 27 47 592 of Kluting. The apparatus of Kluting employs a slip clutch which is interposed between the output element of the transmission and the shaft for the pinions which mate with the toothed racks. The slip clutch is designed in such a way that it is capable of transmitting torque from the output element of the transmission to the shaft for the pinions under normal circumstances but permits the output element to rotate relative to the shaft when the forward or rearward movement of the seat is impeded e.g., by an object in front of or behind the forwardly and rearwardly adjustable seat or by the legs of the occupant or occupants of the seat or seats behind the adjustable seat. Moreover, the torque which the slip clutch can transmit is selected with a view to ensure that the rearwardly moving seat cannot injure an occupant of the seat behind the adjustable seat, i.e., rearward movement of the adjustable seat is interrupted or prevented if the rear part of the seat reaches the leg or legs of a person sitting behind the adjustable seat.
A drawback of the adjusting apparatus of Kluting is that the seat cannot be adjusted at all, or only in response to exertion of a substantial effort, if the motor fails or is out of commission for another reason. A person attempting to shift the seat forwardly or backwards is then required to overcome the resistance which the slip clutch offers to rotation of the common shaft for the pinions. This can present problems, especially to a person occupying the adjustable seat.
German Offenlegungsschrift No. 27 33 484 to Wirtz et al. discloses a seat adjusting apparatus wherein the motor which is used to bring about a change of inclination of the back rest of a seat in a motor vehicle can be detached from the inclination changing mechanism. A screw must be rotated to disengage a clutch disc which normally transmits torque between a common pintle for pivotable leaves forming part of hinges which connect the pivotable back rest to the body supporting portion of the seat and a gear which can be driven by the motor and is rotatable on the shaft. The screw must be rotated by a suitable tool to move the clutch disc axially of the shaft and the screw is rotatably mounted in the shaft. Manipulation of the screw by a screwdriver or a like tool is possible or convenient only when a person wishing to detach the motor from the shaft does not occupy the seat. Moreover, such person is likely to disengage the screw from the shaft instead of disengaging the motor from the shaft. Still further, the motor cannot be used to move the seat forwardly or backwards.